COMPUTER ROOM AIR CONDITIONING

Providing sufficient cooling to ensure that IT equipment operates at maximum efficiency throughout the year presents a number of unique challenges, particularly where the capacity of the equipment is required to grow but space within the server room or data centre is limited.

THE STARTING POINT – MATCHING COOLING CAPACITY WITH HEAT OUTPUT

Servers and other related IT equipment produce a high level of ‘dry bulb’ or ‘sensible’ heat. However, a conventional air conditioning system will remove not only this sensible heat, it will also remove the moisture from the room. This process is known as removing the ‘wet bulb’ or latent heat.

Typically, an air conditioning unit (ACU) rated at 10kw cooling capacity will only remove around 6.2 kw of sensible heat (this may vary from manufacturer to manufacturer). It is therefore imperative that the ACU is specified with sufficient cooling capacity to process all of the sensible heat generated by the equipment.

Failure to provide sufficient cooling capacity will inevitably lead to heat damage or potential failure.

ENSURING YEAR ROUND EFFICIENCY

The heat load within a computer room is relatively constant throughout the year (as the heat gains of the building generally have a small influence upon the total heat load). However, the cooling capacity of the ACU can actually change depending upon the outdoor temperature. For example, when the outdoor temperature is below +15°C the cooling capacity is likely to reduce.

If the outdoor temperature drops below 0°C, part of the system may actually “ice up” or fail altogether (potentially disastrous within a computer/server room). It is therefore essential that the system selected for this purpose is capable of ensuring the cooling capacity in all UK weather conditions.

AVOIDING INEFFICIENT AIR CIRCULATION

Another key challenge is to ensure that the cooling system is configured correctly. Ideally, cool air should be delivered directly to the IT equipment’s intake and the return air extracted close to the equipment’s heat exhaust. This ensures that minimal unwanted heat is recirculated by the equipment.

However, server and computer room layouts can vary significantly, and their configuration can dramatically alter the cooling effect. In some instances, such as where larger or under-floor level fed ACUs are utilised, objects such as cabling or conduit can significantly reduce airflow.

One solution can be the adoption of Hot and Cold Aisles. Heat generated by the IT equipment is rejected into the Hot Aisle, and this hot air is fed through the top of the ACU where it is then passed over a cooling coil which absorbs the heat.

The cooled air is then blown downwards through a floor void before entering the room via grilles positioned to form a Cold Aisle. The cool air is then blown into and sometimes up through the server cabinet, assisted by the integral server fans.

ENSURING OPTIMUM SYSTEM RESILIENCE

Many computer rooms and data centres undertake mission-critical operations, and so optimum resilience is vital.

To minimise the potential for breakdown, Ambient HVAC strongly recommends the adoption of the following measures.

Provision of Back-Up Cooling Capacity

Stand-by cooling capacity of between 50 to 100% of the required cooling capacity should be provided to ensure operational continuity.

Alarm Monitoring and Emergency Response

The computer room air conditioning systems supplied and installed by Ambient HVAC can be configured to provide full alarm ststus, not only for the room temperature but also for each element of the entire system. The provision of stand-by capacity will ensure that, in the event of a system failure, room temperature is maintained at a safe operating level.

Most systems can also be configured to notify both the system operator and Ambient’s Emergency Response Team, which is on hand 24/7, 365 days a year, by SMS, phone dial-up or SNMP signalling.

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